Toutatis (minor planet 4179)

One of the largest near-Earth asteroids
and potentially one of the most dangerous (see potentially
hazardous asteroids. A member of the Apollo
group, it was discovered in 1989 by French astronomers and named (somewhat
inappropriately) after a Celtic god that was the protector of the tribe
in ancient Gaul. Its eccentric, four-year orbit extends from just inside
Earth's orbit to the main asteroid belt; the danger comes from the fact
that the plane of Toutatis's orbit is closer to the plane of Earth's orbit
than any known Earth-crossing asteroid. In December 1992, Toutatis came
within about 4 million km of Earth enabling radar images to be acquired
using the Goldstone Deep Space Communications Complex in California's Mojave
desert. These images revealed two irregularly shaped, cratered objects about
4 and 2.5 km in average diameter which are probably in contact with each
other. Such contact binaries may be fairly common since another one, Castalia,
was observed in 1989. Numerous surface features on Toutatis, including a
pair of large craters, side by side, and a series of three prominent ridges
– a type of asteroid mountain range - are presumed to result from
a complex history of impacts.

Toutatis shows an extraordinarily complex rotation. Whereas the vast majority
of asteroids, and all the planets, spin about a single axis, Toutatis tumbles
around two axes with different periods, of 5.4 and 7.3 Earth days, that
combine in such a way that Toutatis's orientation with respect to the Solar
System never repeats.

On Sep. 29, 2004, Toutatis passed by Earth at a range of just four times
the distance between the Earth and the Moon. One consequence of the asteroid's
frequent close approaches to Earth is that its trajectory more than several
centuries from now cannot be predicted accurately. In fact, of all the Earth-crossing
asteroids, the orbit of Toutatis is thought to be one of the most chaotic.